1. Technical Field
This disclosure relates generally to the field of electrical circuit breakers and more particularly to a mechanical interlock feature that engages upon circuit breaker tripping.
2. Description of the Related Art
In general, circuit breakers are employed to selectively engage a branch circuit to an electrical power supply. This function occurs by engaging and disengaging a pair of operating contacts for each phase of the circuit breaker. The circuit breaker provides protection against persistent overcurrent conditions and against the very high currents produced by short circuits. Typically, one of each pair of the operating contacts are supported by a pivoting contact arm while the other operating contact is substantially stationary. The contact arm is pivoted by an operating mechanism such that the movable contact supported by the contact arm can be engaged and disengaged from the stationary contact.
There are several ways by which the operating mechanism for the circuit breaker can disengage the operating contacts: the circuit breaker operating handle can be used to activate the operating mechanism; or a tripping mechanism, responsive to unacceptable levels of current carried by the circuit breaker, can be used to activate the operating mechanism; or auxiliary devices can be used to trip the circuit breaker thereby move the movable contact. For many circuit breakers, the operating handle is coupled to the operating mechanism such that when the tripping mechanism activates the operating mechanism to separate the contacts, the operating handle moves to a fault or tripped position.
When an overload condition occurs, the trip bar is rotated away allowing the trip bar latch to disengage the auxiliary latch. With the auxiliary latch free, the cradle is able to pivot thereby disengaging the breaker contacts. This sequence of event is referred to as the breaker tripping. In order for the breaker to be safely reset, the auxiliary latch must be held open until the cradle is first reset. According to the prior art, a variety of heavy springs and dampers are used to keep the auxiliary latch from resetting prematurely. In addition a push to trip button could be used to trip the mechanism again.
The disadvantage of the prior art systems are that there is no guarantee that the auxiliary latch will not reset after the breaker is tripped. In addition, using some type of damper will add extra cost to the mechanism. Using a heavier torsion spring could make the auxiliary latch rebound thereby allowing itself to reset with the trip bar latch. The cradle could not be reset in this case as it would strike the top of the auxiliary latch.
Accordingly, there is a need for a secure feature that will prevent the auxiliary latch from resetting prematurely.